Classification of neurocysticercosis based on location and appearance of the parasite and surrounding host tissue on neuroimaging

Form*	Characteristic on neuroimaging	Histopathology
Parenchymal^¶
Nonviable calcified	Nodular calcifications <20 mm in diameter (often 1 to 5 mm) with or without surrounding edema and/or contrast enhancement.	Calcified granuloma with or without surrounding inflammation and/or gliosis.
Single, small enhancing	Cystic or nodular enhancing lesion <2 cm in size.	Single parenchymal parasites in the process of degeneration with surrounding inflammation and variable opacification or absence of the cyst fluid.
Viable parenchymal	Vesicular lesions often with evidence of associated contrast enhancement and/or surrounding edema. The scolex is often visible on high-definition imaging.	Parasites with intact cyst wall, vesicular fluid, and scolex, with variable amounts of inflammation surrounding the parasite sometimes invading the cyst wall.
Extraparenchymal^Δ
Intraventricular	Cysticerci within the ventricles, obstructive hydrocephalus or loculated hydrocephalus with disproportionate dilatation of the ventricles in CT/MRI (suggestive of a cysticercus).	Viable cysticercus cyst within the ventricle and/or obstructive hydrocephalus.
Subarachnoid	Cysticerci in the Sylvian fissure, in the basilar cisterns, or interhemispheric spaces. Strokes or meningitis without discrete cysts.	Cysticerci in the subarachnoid space often with arachnoiditis, vasculitis. The cysticerci are often in clusters with proliferating membranes (racemose) and may lack a scolex.
Spinal	Cysticerci within the spinal subarachnoid space with or without evidence of inflammation/diffuse spinal arachnoiditis. Intramedullary cysticerci within the spinal cord.	Subarachnoid cysticerci often with associated arachnoiditis. Intramedullary cysticerci similar pathologically to parenchymal cysticerci.

CT: computed tomography; MRI: magnetic resonance imaging.
* Patients with more than one form are classified with the form found lower on the chart, with the exception that single enhancing lesions that are also viable are grouped with single enhancing lesions. Ocular cysticercosis is classified separately.
¶ Refers to cysticerci in the brain parenchyma. Small cysticerci in the gyri over the cerebral convexity behave clinically like parenchymal cysticerci and are grouped with parenchymal cysticerci. Rare forms of neurocysticercosis include multiple inflamed parenchymal cysticerci with diffuse cerebral edema, termed cysticercal encephalitis, large parenchymal cysticerci (>20 mm).
Δ Refers to cysticerci in the central nervous system outside of the brain parenchyma.

Reproduced from: White AC Jr, Coyle CM, Rajshekhar V, et al. Diagnosis and treatment of neurocysticercosis: 2017 clinical practice guidelines by the Infectious Diseases Society of America (IDSA) and the American Society of Tropical Medicine and Hygiene (ASTMH). Clin Infect Dis 2018; 66(8):e49-e75, by permission of Oxford University Press on behalf of IDSA and ASTMH. Copyright © 2018. Available at: https://www.idsociety.org/practice-guideline/neurocysticercosis/.

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Classification of neurocysticercosis based on location and appearance of the parasite and surrounding host tissue on neuroimaging